1. Field of the Invention
The present invention relates to a video endoscope system used in medical applications to obtain images of a surface of a subject illuminated by visible light and images of the subject through autofluorescence resulting from excitation light and specifically relates to an optical system for the light source device that generates illuminating light and excitation light to supply them into the video endoscope. The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-227328 (filed on Jul. 27, 2000), which is expressly incorporated herein by reference in its entirety.
2. Description of the Related Art
In recent years, a method has been proposed for observing the autofluorescence of a subject (specifically, body cavity wall) with a video endoscope systems. In a body cavity wall irradiated by light of a specific wavelength (generally ultraviolet light), the tissues are excited to emit fluorescence. The intensity of the fluorescence generated by healthy tissue is stronger than that generated from unhealthy tissue, such as cancerous tissue. This causes an intensity distribution of autofluorescence in the body cavity when the cavity includes unhealthy tissue. capturing images of autofluorescence from the body cavity wall with the solid state image sensing device (CCD) of the video endoscope makes it possible to observe special images of the body cavity wall that differ from images of the body cavity wall obtained by normal illumination with visible light.
As such video endoscope systems that allow the fluorescence observation, a video endoscope system of the so-called RGB frame sequential system is used, which has an RGB rotating shutter for separating white light (visible light) emitted from a light source into red, green, and blue light components, an illumination optical system for transmitting in sequence the red, green and blue light to the proximal end of the video endoscope and an ultraviolet source for supplying ultraviolet light to excite the body cavity wall into the above-mentioned illumination optical system. FIG. 7 shows an optical configuration in the light source device 60 of such a video endoscope system. FIG. 8 is a front view of an RGB rotating shutter 603 and a UV rotating shutter 609 in the light source device 60.
As shown in FIG. 7, the light source device 60 is composed of a white light source 601, an infrared cut-off filter 602, the RGB rotating shutter 603, a UV reflection filter 604, a light aperture diaphragm 605, a condenser lens 606, an ultraviolet light source 607, a UV transmission filter 608, the UV rotating shutter 609, and a mirror 610.
The RGB rotating shutter 603 is, as shown in FIG.7 and FIG. 8A, a disc coaxially mounted on a drive shaft of a motor 603a, on which are formed three fan-shaped window, respectively fitted with red, green and blue filters 603b-603d. These filters 603b-603d are band pass filters, respectively transmitting red, green and blue light and arranged side by side at predetermined intervals on the same circle coaxial with outer edge of the disc. These filters 603b-603d are arranged to occupy almost a semicircular area within this circle.
As shown in FIG. 7 and FIG. 8, UV rotating shutter 609 is a disk coaxially mounted on a drive shaft of a motor 609a, on which are formed a fan-shaped opening whose apex coincides with the center of the disc. The central angle of the opening 609b is slightly less than 180 degrees.
As shown in FIG. 7, the collimated beam of white light emitted from the white light source 601 is deprived of its wavelength components in the infrared region by the infrared cut-off filter 602, transmitted through one of the red, green or blue filters 603b-603d provided on the RGB rotating shutter 603 and the UV reflection filter 604, and subsequently adjusted to have a proper amount of light by the light aperture diaphragm 605, and focused onto a proximal end face 70a of a light guide 70 of the video endoscope by the condenser lens 606.
The collimated light beam consisting of wavelengths in the ultraviolet region emitted from the ultraviolet light source 607 in a direction parallel to the collimated beam of white light is filtered by the UV transmission filter 608 to be a collimated beam having wavelengths only in the ultraviolet region, then transmitted through the opening 609b formed on the UV rotating shutter 609, then sequentially reflected by the mirror 610 and the UV reflection filter 604 to shift to trace the same optical path as the above-emitted collimated beam of white light, subsequently adjusted to have a proper amount of light by the light aperture diaphragm 605, and focused onto the proximal end face 70a of the light guide 70 by the condenser lens 606.
The RGB rotating shutter 603 and the UV rotating shutter 609 are rotated by the motors 603a and 609a, respectively, whose speeds and rotation phases are controlled, so that a beam consisting of a blue component (blue light), a beam consisting of a green component (green light), a beam consisting of a red component (red light), and a beam having wavelengths in the ultraviolet region (ultraviolet light) are incident onto the proximal end face of the light guide 70, in turn. FIG. 9 gives a schematic representation of these respective beams incident on the condenser lens 606. In FIG. 9, an interval designated by two broken lines indicates a period in which the rotating shutter 603 and the rotating shutter 609 round in synchronism with each other, with periods corresponding to protruding portions of the lines in the graph indicating periods in which the collimated beam of white light enters one of RGB filters 603b-603d or a period in which a collimated light beam consisting of the wavelengths in the ultraviolet region streams into the opening 609b, respectively. A symbol xe2x80x9cxxe2x80x9d appearing on each line indicates a blank period in which no beam enters the condenser lens 606.
As shown in FIG. 9, while the rotating filter 603 and the rotating shutter 609 round, blue light, green light, red light, and ultraviolet light are sequentially onto the condenser lens 606. Here, since the fan-shaped opening 609b formed on the UV rotating shutter 609 has a larger center angle than the center angles of each of the three fan-shaped windows formed on RGB rotating shutter 603, the period when ultraviolet light is incident on the condenser lens 606 is longer than any one of periods for blue light, green light and red light.
Light of each color that enters the light guide 70 from the proximal end face 70a thereof is transmitted through this light guide 70 to its distal end face to illuminate or irradiate the body cavity wall through a light distribution lens fitted onto the distal end of the video endoscope (not shown in the figure). Images of the body cavity wall illuminated sequentially by the blue light, the green light, and the red light which are formed by an objective optical system (not shown in the figure), and an image of autofluorescence of the body cavity wall that is excited by the ultraviolet light which is formed by the objective optical system (not shown in the figure) are sequentially picked up by the CCD installed in the video endoscope, converted into electronic signals, and sent to an image signal processing circuit within an endoscope processor (not shown in the figure).
In the optical system of the above-mentioned light equipment 60, the two light sources 601, 607 are arranged side by side so that a collimated beam of white light and a collimated beam consisting of wavelengths in the ultraviolet region are parallel to each other. These two collimated light beams are guided to a common optical path through the mirror 610 and the UV reflection filter 604. Thus, these two beams share light aperture diaphragm 605 and condenser lens 606.
However, a configuration in which two collimated light beams emitted from two light sources 601, 607 are arranged in parallel needs a large total number of optical elements. This leads to increased mass and bulk of the optical system and the whole light source device as well. Additionally, the fact that several optical elements such as mirrors are used to reflect the beam multiple times requires an excessive amount of time to adjust optical axes of the optical system.
Moreover, UV reflection filter 604 shown in FIG. 7 is required to transmit the beam of white light efficiently, and to reflect the beam consisting of wavelengths in the ultraviolet region efficiently, otherwise, light sufficient to illuminate or excite the subject (the body cavity wall) cannot be introduced into light guide 70.
It is the main object of the present invention to provide an optical system for a light source device for a a video endoscope system that can meet the purpose of the device, but with fewer optical elements, and that enables an operator to adjust optical axes easily and relatively quickly, without consuming excessive time. An additional object of the present invention is to provide a optical system for a light source device such that a UV reflection filter allows a beam of white light to pass therethrough efficiently, while also reflecting a beam consisting of wavelengths in the ultraviolet region efficiently.
The optical system according to present invention devised to resolve the above-described problem has a condenser lens for converging a light beam onto a proximal end face of a light guide, a visible light source that emits a first collimated light beam having wavelengths in a visible region and is arranged so that the first collimated light beam is incident on the condenser lens, an ultraviolet light source that emits a second collimated light beam having wavelengths in an ultraviolet region and is arranged so that the second collimated light beam intersects the first collimated light beam orthgonally, and a UV reflection filter arranged at a position where the first collimated light beam and the second collimated light beam intersect. The UV reflection filter is inclined to each collimated light beam at an angle of 45 degrees, transmits the first collimated light beam, and reflects the second collimated light beam toward the condenser lens.
By this arrangement, the first collimated light beam that was emitted from the visible light source and has wavelengths in the visible region is transmitted through the UV reflection filter to enter the condenser lens, and the second collimated light beam having wavelengths in the ultraviolet region is reflected by the UV reflection filter by 90 degrees to enter the condenser lens. Thus, the second collimated light beam having wavelengths in the ultraviolet region is reflected only once to enter the condenser lens, so that the number of the optical elements can be reduced. As a result, the adjustment of the optical axes can be done easily.
Because the UV reflection filter is inclined to both collimated light beams at an angle of 45 degrees, the UV reflection filter transmits the first collimated light beam having wavelengths in the visible region, while efficiently reflecting the second collimated light beam consisting of wavelengths in the ultraviolet region. This configuration of the optical system makes it possible to introduce sufficient amount of light to illuminate or excite the subject (the body cavity wall) into the light guide.